Telephone-exchange system



w. w. CARPENTER y TELEPHONE EXCHANGE SYSTEM Filed Sept. 21, 1923 4 Sheets-Sheet l June 2, 1925'.

June 2, 1925. /r 1,540,054

W. W. CARPENTER TELEPHONE EXCHANGE SYSTEM Filed Sept. 2.1n 1923 4 Sheets-Smet l2' Waffe/7 W aye/#eff June 2, 1925.

1,540,054 W. W. CARPENTER TELEPHONE EXCHANGE SYSTEM Filed Sept. 21, 1923 4 Sheets-Sheet 3 y WH" #E ...Kg

/m/e/f/a/t' Waffe/7 W Caffe/Wr.

June 2, 1925- 1540;()54 W. W. CARPENTER I TELEPHONE EXCHANGE SYSTM Filed Sept. 2l, 1923 4 Sheets-Shet 4 i (/mfd an 0 ere/ Patented .lune 2, 1925.

'Human STATES im,TENT,OH-ICE.

WARREN CARPENTER, AOF QUEENS, NEW YORK, .rSSIG-N/` `TO WESTERN ELECTRIC COMPANY, INCORPORATED; Oli. NEM? YORK, Ni Y., A CQRPORATION, 0F NEW YORK.

TELEPHONE-EXCHANGE SKYS'IElVL Application med september 21, 1923. serial Nofceasez.

T 0 all l07mm it may Concern:

Be it known that I, TARREN W. CARPEN- TER, a citizen ot the United States of America, residii'ig at Queens, in the county of Queens and State ot' New York, have in vented certain new and useful Improvements in Telephone-Exchange Systems, of which the following isa full, clear, concise, and exact description.

This invention relates to multi-exchange telephone systems and more particularly to two-way interexchange trunk circuits theretor.

The object of the invention is to improve .the operating efficiency ot circuits ot this character.

A Vfeature of the invention is a circuit a1"- rangement whereby an established connec-` tion betweenoperators at opposite ends of a trunlf: line is momentarilybroken down and reestablished'in the opposite direction in case the operator originating the connection chashes, that is, alternately disconnects `from and connects to the trunk for the purpose ot attracting the distant operator-sattention, whereby improved supervision and operation of devices Jfor holding the trunk line busy during the flashing interval'is secured over circuits of the character described having relatively low resistance leaks to ground.

More specifically, `when the operator originating the connection' removes and reinserts herconnecting plug, a battery, which was included in a relatively low resistance bridge across the trunk at the originating or calling end when the connection was irst established, is removed and a similar battery connected in a relatively low resistance circuit across the distant or called end o l the trunk which in effect is the saine condition as would Vbe created if the` connection had been originated at that end of the trunk. The continued removal and insertionofv the originating operato'rs plug then causes the resistance of the bridgecircuit at the calling 4end to be alternately increased and reduced suiliciently to cause the alternate release and operation oi a relay in the battery circuitat the called end oit thetrunl, whiclrrelay controls asupervisory signal appearing before the. operator. `During the interval between the removal and reinsertion of the plug, a

y busyguard is placed'on the trunk to prevent its being seized by another operator or autolniatic switch.

Other features not specifically mentioned i above will more readily appear 'from the following description and drawings, in which a trunk circuit einbodyingthe invention is shown together with sufficient connecting apparatus to properly illustrate the one `end ot animer-exchange trunk lineterf i minates. i Y

Figs. Sand 4 show a portion ot a similar exchange at the 4distant end of the trunk.

At each exchange provisions are made for terminating dial station lines in'autoinatic switches, not shown, which switches have access to both the operator and the trunk. vFigs land 4L sho-w` incoming selector switch circuits at the two exchanges arranged to be controlled by current'impulses transmitted over the trunk circuit from lthe operator at the distant exchange,` Figs. 3

'and 4, and accordingly inserts the plug 200 oit' her cord circuit in the jack 201 associated with the trunk Ln L2. V

lhen plug AP was inserted in the jack ot the calling `line it will be assumed that ground was encounteredon the sleeve of the jack thereby causing the lighting o1 supervisory lamp C in an obvious circuit. Super-. visory lampk A does not light'iflit is assumed that a call was awaiting the insertion of plug AP asin such a case the answering cord supervisory relay AS operates in an obvious circuit including the closed loop of the calling line, thereby disconnecting lampl A at the back @eilte-Ct ofthe relay, .Ilarnpy C continues to burn after plug 200 is inserted in jack 201 and until the called operator answers as will later appear. n

TWhen the plug 200 isinserted in the jack 201, relay 202 operates in the following circuit, battery, relay 202, contacts 203 of jack 201, contacts 204 of relay 205, and contacts 206 of relay 207 to ground. Relay 202 in operating, closes its contacts 208 thereby closing a locking circuit for itself which may be traced from battery, winding of relay 202, contacts 203 and 208 to ground. Relay 202 in operating, also closes operating circuits for relays 209 and 210 The circuit for relay 209 can be traced from battery, winding o1 relay V209, and contacts 211 of relay 202 to ground. The circuit for relay 210 is traced from battery, through the winding of that rela-y, contact 212 of relayV 213 and contact 214 otrelay 202 to ground. ,Relay 209 in operating, connects ground through its contacts 215 to the sleeve conductor 247 leading to the multiple terminals CM of a connection switch not shown, thus putting a busy condition on the test terminal of the switch to prevent the trunk from being seized in case a dial subscriber attempts to call the distant exchange. Closure of contacts 215 also supplies ground to operaterelays 216, 207 and 217, the circuits r'or which are as follows: In relay 216, the circuit eX- tends from battery, through the'winding of that relay, and theV contacts215 of relay 209 to ground, and for relays 207 and 217 parallel circuits entend from battery, through the windings of these relays, contacts 218 of relay 219, contacts 220 of relay 221, contacts 222 of relay 223 and contacts 215 of relay 209, to ground. Relay 216 operated connects ground to the sleeves of the trunk aclrs as a busy guard. Relay 207 in closing its contacts 224 completes a locking circuit for itself which may be traced from battery, winding and contacts 224 ot relay 207, contacts 222 of relay 223 and contacts 215 o't 'relay 209 to ground. Relay217 is also held to ground tln'ough the above traced circuit. Relay i207 in operating, also closes an energizing circuit for relay 225 which may be traced from battery, winding of relayl225, contacts 226 of relay 227, and .contacts 228 of relay 207 to ground. Relay 225 in operating, closes an obvious energizing circuit 'for relay 219 and also connects direct ground at its contacts 229 to hold relays 207 and 217 energized for a reason which wiii later appear. Relay 217 in operating, completes va circuit for connecting relays 230 and 231 in series withrelay 330 at the distant end of the trunk which can be traced from battery, relay 231, contacts 234 of relay 217, contacts 235 of relay 210,.contacts 236 of relay 223,' lower right winding of repeating coil 233, conductor L2. lower left winding oit' repeating coil 333, contacts 336 of relay 323, contacts 338 of relay 307, contacts 339 of' relay 340, contacts 337 of relay 310, contacts 341 of relay 317, winding 01:; relay 330, upper left winding of repeating coil conductor L, of the trunk, upper right winding of the 'repeating coil 233 (Fig.i2)`winding of relay 230 and contacts 232 of relay 217 to ground.

Relay 330 at the distant end of the trunk in operating, prepares the equipment thereat for receivingA the impulses to be sent, by closing the circuit for the pulse relay 400 (Fig. 4) oi the incoming selector, the circuit oi' which can'be traced from grounded battery,r left-hand winding of relay 400, contacts y401 of relay402, conductors 404 and 351, contacts 342 of relay 343, winding of relay 321, contacts 344 of relay 305, contacts of relay 330 and contactsl 346 or relay 317 to ground.v Relay 321v operates in this circuit and connects ground to the sleeve conductor 347 thus placing a ,busy-condition on the test terminals CM of a connector'switch (not shown) to prevent the trunk from being seized by a dial subscriber. This circuit can be traced from ground, contacts 348 of relay 321 andl contacts 3220i relay 323 to conductor 347. Ground on the conductor 347 y also operates rela-y 316, which in operating, connects ground to the sleeves of the trunk jacks as a busy guard. Relay 321in operab ing, also closesa circuit forv the operation of relay 325 which canbe traced from battery, relay 325 and contacts 349 to ground. Relay 325 in operating, closes at its contacts 350 an obvious circuit for theenergization of relay 319. The closure of contacts 329 of'relay 325 also connects ground at this point to conductor 347 thusholdinga busy condition on the connection switch `multiple CM for a short time after the release of relay 321 due to the fact that relay 325 is slowto-release, which will be referred to later.

Relay 319 in operating. closes a circuit for the operation of relay 403 which can be traced from battery, relay 403, conductors 405 and 352, contact 353 of relay 343', contacts V354A of relay 319 and contacts 346 of relay 317 to ground. n A K,

Relays 400 and 403 now being energized, the selector is ready to receive pulses and the next step is the operation at the calling eX- change of the dialing key 255 which closes an obvious circuit for the operation ofrelay. 21,3'and lights the dial pilot lamp 256. Relay213 in operating, transfers theground for holding relay 210 operated, from contacts 214 of relay"202,'to contacts 257 of dial 258. Relay 213 in operating, also closes at its 'contacts 259 and 260 short circuits around the upper and lower right hand windings respectively of Nrepeating vcoil 233.

It will be assumed that Zero is the digit to be dialed to signal the distant operator. ll/Then the .dial 258 is operated, the im-y pulse contacts 257 interrupt a circuit through relay 210 and as the dial returns to normal, relay 210 releases and operates in unison therewith. VThe first time relay 210 releases, the trunk line loop circuit 'through relay 230, 231 and 330 previously traced, is opened at contact 235 thus releasing relays 230 and 330. Relay 230 in releasing, performs no useful function at thistiine. As relay 210 releases and closes its contacts 237, a circuit is closed for the operation of relay 227 which can be traced as follows: battery, winding of relay 231, contacts 234 of relay 217, contacts 237 of relay 210, winding `of relay 227 and oontacts 261 of relay 217 to ground. Relay 227 operates in this circuit and .relay 231 is held operated. Relay 231 is sluggish `and therefore does not release during the period between the opening of contacts 2351and the closing of contacts 237. Relay227 in operating, opens at itsV contacts 226 the energiz-` ing circuit of relay 225 but since this relay is sluggish, it holds kup-over the dial pulses. Relay 227 in operating, also connects battery through resistance 262, to the conductor L2 of the trunk, thus reoperating relays 230 and 330. This circuit may be traced from bate tery, resistance 262, contacts 263 of relayv 227, contacts 236rof .relay 223, contact 260 of relay 213 Vto conductor L2. It will be noted that the trunk loop is opened and relays 230 and 330 released only during the interval between the release of relay 210 and the operation of relay 227. When cone tacts 257 of the dial again `close relay 210 `is reoperated and the circuit through the wind`- ing of relays 227 and 231 is opened at contacts 237. When contacts 235 of relay 210 close, relays 230 `and 3 30 are connected in series withrelay 231 to battery againinstead of through resistance 262 which is disconnected upon the release of relay 227.` Relay 227, however, does ynot lrelease until 4after contact 235 of relay 210 closed due to the charging of condenser 264 bridged across the contact 237 thereby prevent-ing a false impulse being sent `out due to the relcaseof relay 227 before `contacts 2350i? relay 210 close. The above cycle of operation occurs for each impulseV sent from the fdial thus lrelaying vthe impulses over the trunk to the distant incoming selector or connector which advances :the .automatic mechanism ltherea-t tothe desired level which, in the `system described, is assumed to be the .tenth or zero level.

The operation of the selector switch (Fig. 4) in response to the alternate operation land release of relay 400, will not be Adiscussedfin detail as the operation fof such apparatus is wellknown to those familiar with automatic telephone circuits, it ybeing sufficient lfto mention that the vertical magnet 406 `is'operated when relay 400 releases on the first'irn terruption of the dial contacts257 in al circuit whichrcan be traced as follows: battery,

vertical magnet 406, relay 408, contacts 407 y of relay 400, contacts 409 of relay 402, and contacts 410 of relay 403 to ground. This operation of magnet 406 is repeated with each dial interruption Vthus stepping the switch upward to the desired level which as before stated, is-assumed to bey the tenth or zero. level, thisbeing the yposition of the switch in which thecontacts 411 vare adapted to be closed. i l 1` y l lhen dialing is completed the ldialing-key is restored to normal thus releasing therelay 3 213 and extinguishing the dial pilot lamp 256. When relay 213 releases, the shunt cir cuits around the righthand windings of rcpeating coil 233, previously ,traced are removed, and the holding circuit forrelay 210 is transferred back to and under control of relay 202. This holding circuit now extends ating, also opensV at its contacts 342 the cire` cuitfor relays 321 and 400, lwhich v:relays now release. At its contacts 353 relay 343` opens the circuit for relay 403 which also releases and at its left armature 1 and baclr cont-act completes` an obvious-circuit 'of the operation of release magnet 413 which then functions to restore ythe switch to normah `Vh'en `relay 343 .operates `it further closes a Y circuit for line lamp 367 which can be traced from battery, contacts 368 and 369 of relay 309, .contacts y366 of relay 343 and lamp 367 to ground, thus giving the :operator-Ian ifndfi-V cationof the call.- When relay 321 released it connected ground to operate relays 371, 305 'and 340, the circuits for which vcan be traced from ground, through 'contacts 372 of relay` 321, contacts 373 of relay 319, contacts 374 of relay 331 and thence in parallel circuits `to battery, one circuit extending through contacts y375 of relay 3117 and winding of relay r305 :and the Aother through the windings ofV relays137l and 340. These rei lays now operate and :loch to ground through contacts 376 :of relay 371, 373 of relayv 319 and 372 of relay 321). `Vhen relay 305`operates it provides a liold'ing circuit for relay 325 whichwould otherwise be yreleased due to the release lof relay A321. This holding circuit canJ-'be ytraced from battery, winding of relay`325, contacts 377 vof relay 305, con tacts 345 of relay 330 and contacts `346=of relay 317 to ground. Vlt'will `be noted that due to the fact that relay 325 isislow to reizo leasev the aboye'vtrac'ed holding circuit is .no l

closed before relay 325 and relay 319 controlled by it have time to release. l/ilhen relay 3A0 operated it closed its contacts 373 thus connecting the upper or tip terininal ot the right-hand winding of repeating coil 333 to Vthe open contacts 379 ot relay 302, the lower or ring terminal being` permanently connected to contact 330. Relay 340 in operating also opensits contacts 339, thus breaking the shunt connection normally` around high resistance relay 331 and relay 327 and thereby inserting these relays in series with relay 330 which increases the trunk loop resistance to such a value that relays 230 and release. Relay 231, in releasing, closes a circuit for the operation or relays 240 and 271 whichfc'an be traced from battery, winding Vof relay 2&0, winding of relay 271, contacts 274 of relay 231, contacts 273 of relay 219 and contacts v272 of relay 221 to ground.` Relays 241- and 271 operate and lock to ground throughcontacts 276 ot relay 271, contacts 273 otrelay 219, and contacts 272 ot relay 221. ARelay 240, in operating, closesits contact-s 273 to connect the upper or tipk terminal of the lett-hand winding of repeating coil 233 to the tip contacts of the jack 201 and plug 200, over the contacts 279 of operated relay 202.'A The lower or ring terminal ot. repeating coil 233 is permanently connected to ycontact 230, which Ain this case is closed thus connecting the tip and ring of the cord to the repeating coil. I

The operator at the distant end of the trunk upon observing the illumination of lanip 367 inserts plug Alwin jack 301 and relay 302 operates in the following circuit: battery, winding of relay 302, contacts 303 Aor" j aclr 301 and contacts 382y of relay 343 to ground. Relay `302, in operating, locks to ground at its contacts 303 in an obvious circuit and closes a circuit for-the operation of relay 310 which can lbe traced from battery, winding of relay 310, contacts 312 of Vrelay 313 and contacts 314 of relay 302'to ground gy relay 302 in operating also closes a' circuit for .relay 309 which can be traced trom battery through the relay 309 andftoground at contacts 311 of relay' 302. Relay 310, in Opf erating, again shunts relays 331 and 327, thusreducing the trunk line loop resistance toa point where relay 231 at the originating end 'of the trunk will again operate. The above shunt circuit can be traced from line conductor L2, lower.lett-winding of the repeating coil 333, contacts 336 of relay 323, contacts 335 of relay 310, contacts 34:1 oi' relay 317, relay 330, upper lett winding of repeating coil 333 to line conductor L1. Relay 309 in operating closes a circuitto operate the supervisory relay-334in series with the operators answering cord supervisory relay AS which circuit can be traced from ground supplied through the upper winding` of retardation coil RG', over the coil RC to grounded battery. The cord supervisory relay AS operates in this circuit and at its back contact 'opens the circuit for the cord supervisory lamp A which would otherwise be lighted in a circuit from battery through larnp A the back contact of relay AS and groundon the sleeve of jack 301 placed there when relay 316 operated. The talking battery connection tor the called operator is now completed and the operator is' connected to the switchboard side of the trunk repeating coil. It will be obvious that callingsupervisory lamp C will remain lighted untilv the ystation called over plug 300l answers.-

Relay 231 at the outgoing end'of thetrunk in reoperating closes a circuit to operate the supervisory relay'234 in series with the operators calling cord supervisory relay CS, which circuitcanbe traced` from ground through the upper winding of retardation coil RC, tip ot the plug 200, tip contact of j ack 201,* contacts 27 9ct relay 232, contacts 273 of relay 240, upper lei't winding of repeating coilr 233, upper winding of retardation coil 233, winding of relay 2311, contacts 235 of relay 231, contacts 237 of relay 209, lower winding ot' retardation coil 233, lower Aleft winding of repating coil 233, contacts 230 of relay'202,`ring contacts of jack 201 and plu'g'200 and over the ring conductor of the cord through the V'cord supervisory relay CS and lower winding of retardation coil RC to'grounded battery; The cord supervisory relay CS operates in this circuit and at its back contacts opens the circuit of supervisory lainp C which goes out. The talking battery circuit for the calling operator is now completed and she is connected to the switchboard side of the trunk repeating coil. The connection is now complete between the calling and called operators.

Flash/ing.

.Incase the caling operator'Figs. 1V and 2 should find it necessary to flash, i. e., signal the called operator before theconnection is lilo . cause the release of relays 209 and 210.

When relay 210 releases, the battery bridge across the trunk including` relays 230 andv 231 is nimnentarily` interrupted at contacts 235 and a circ-uit is closed at` cont-acts 237 to operate relay `227 and hold 231 operated, which can be traced from battery, Winding ot relay 231, contacts 234 ot' relay. 217, con` tacts 237 ot relay 210, Winding ot' relay 227 and to ground at contacts 261 of relay 217. Relay 227, in operating, places a substitute battery bridge across the trunlt which can be traced 'from battery, resistance 262;, contacts 263 ot relay 227, contacts 236 ot relay 223, lower right Winding' of repeating coil' 233, over trunk conductor L2, through the low resistance bridge including relay 330 at the. distant end, back over trunk conductor 11 upper right-hand Windingk of repeating coil 233,'

winding of relay 230V to ground at contacts 232 of relay 217. Relay 227, in operating, alsoreleases relay 225, which in turn, releases all the other operated relays. l/Vhen relays 217 and 227 released, battery and ground was disconnected from the trunk and a dryor battery freev bridge includingl relay 230 was substituted therefor. This circuit can 'be traced from the upper right Winding of repeating coil233, Winding of relay 230, contacts 241 ot relay 217', contacts 237 of relay 210, contacts y239 ot relay 240, contacts 238 of relay 207, contacts 236 of relayl 223 to the loWer Winding of repeating coil 233. yIn case the plug` is rcinserted during the release of the above relays, the circuit does not function and the relay 202 cannot operate as its operating ground' is open at the contacts of relays 205 and 207. c

lVhen relays 217 and 227 released, thus removing battery and ground' from the trunk, relay 330 at the distant end of the trunk released, which in turn, opened the locking circuit for relay 325, which in turn caused relays 319, 371, 340, 305, 343 and k384 to release. When relay 319 releasedjit closed at its contacts 318 a circuit to operate relays 317' and 307 which may betraced from ground, contacts 315" of relay 309, contacts 322 ot' relay 323, contacts' 320 of relay 321, contacts 318 ot relay 319 and thence .over parallel paths through thewindings ot relays 307 andV 317 to battery. When relay 317 operated, battery was connected to one side of the trunk L2 through relay 331 and ground Was connected to conductor L1 through relay 330,I thus completing the following circuit: battery, Winding of relay 331, contacts 334 of relay 317, contacts 335 of relay 310, contacts 336' of relay l323, lower left winding of repeating coilvr 333, conductor ML2, lower right Winding of rrepeating coil 233", contacts236 of relay 223, contacts 238 of relay 207, contacts 239 of relay240, con

llamp A.

tacts 237 `of relay 21`0,'co`ntacts 241 of relay 217, Winding'v ot relay 230, upper right Winding of repeating coil 233 to conductor L thence over the trunk to the upper lett Winding "ot" repeating coil 333, through the Winding of relay 330 and contacts 332 ot relay 317 to ground. Relays 330 and 331 at the called or distant end of the trunk and relay 230 at the calling end oitl` the trunk operate. c i

It will be noted that battery is novv connected to the trunk at the distant or'called end instead ot at the calling end ofthe trunk, that is toA say, instead of having a dry or battery treebridge at the called or distant end of the trunk and a Wet or battery bridge across the trunk at theoriginating or calling end, this vsituation is now reversed andthe bridge across-the called end includes battery in series with relays 330 and 331,

'While' the battei'yin series with relay 230 the calling endl has been removed, together with relay 231.

With the release ot relay 340 the operators answering cord supervisory relay AS releases, thus lighting the cord supervisory The talking battery circuit at that end ofthe trunk is also broken at the contacts of relay 340 When it operates.

The operation ot relay 230 at the calling exchange in series With distant relays 330 and 33 1 just mentioned, causes relay 221 to operate inseries With relay ot the selec-'- tor circuit,y which circuit can be traced from battery, Winding of relay 100, contacts 101 of relay 102, conductors 104 and 251, contacts 242 of relay 243, Winding of relay 221, contacts 244 ot relay 205, contacts 245 ot relay 230 and to ground at contacts 246 of relay 217. Relays 221 and 100 operate, but the operation -ot relay 100 accomplishes ,no useful purpose atl this time. Relay 221, in operating,l causes the operation `of relay 216 by closing a circuit Which can be traced from battery, Winding ot relay 216, contacts 222 of relay 223 and contacts 248V of relay 221 to ground. Relay 216, in operating, closes an obvious circuit toconnect ground to the sleeves of the trunk jacks. It Will be evident also that the ground supplied to operate relay 216 is also extended over conductor 247 tothe multiple terminals CM of aiconnector switch, not shovvn, to prevent the trunk from being seized by a dial station K, call.

Relay 221, in` operating, also connects ground at its contacts 249 to operate relay 225l in lan obvious circuit, Relay 225, in operating, closes an obvious circuit to operate relay 219. Relay 219, in operating,

4closes a circuitto operate relay 103v in the selector circuit, Fig. 1, rvhich circuit can be traced from battery, WindingA of relay 103, conductors 105,y and252, contacts 253 ot relay 243, contacts 254 relay 219 and lofi to ground kat contacts 246 of relay Relay 225, in operating, also connects ground atA its contacts 229 to maintain a busy con- Cil dition on conductor 247 leading to the connector multiple CM. The withdrawal of the plug also causes relay CS in the cord to release thus lighting lamp C.

l/Vhen the calling operator reinserts the plug for the lirst time, relay 202 operates to ground -at contacts 205 of relay 207 as heretofore described. Relay 202 in closing its contacts causesfthe operation of relay 209 in an obvious circuit and also the operation of relay 210, the circuit for which can be traced from battery, Winding of relay 210, contacts 212 of relay 213 and to ground at contacts214 of relay 202. Relay 209, in operating, closes a circuit to operate relay 243 which can be traced from battery, winding ot.' relay 243, contacts 289 of relay 240, contacts 290 of relay 209, contacts 291 ot relay 207 and to ground at contacts 292 of relay 219. Relay 243, in operating, looks to ground in the following circuit: battery, winding of relay 243, contacts 270, contacts 254 of relay 219 and contacts 246 of relay 217 to ground. Relay 24.3, in operating, also opens atv contacts 242 .the energizing circuit ior relay 221 and relay 100 in the selector circuit, both oi which relays release. -Re lay 221 is slow in releasing, but `when released, causes the operation of relays 240, 205 Vand 271, the circuits for which-can be traced `from ground oncontactsf272 ot relay 221, contacts 273 of relay 219, contacts 274 of relay 231 and thence over parallel circuits to battery; one of which errtends through the windings of relays 271 and 240 and the other, through contacts 275 ot relay 217 and the winding of relay 205. Relays 271, 240 and 205 operate. Relay 225 being slow to release does not retract its armature immediately upon the release of relay 221 and, therefore, it is held up to ground at relay 217 as soon as relay 205 operates. This holding circuit can be traced from battery. winding of relay 225,'

contacts 277 ot relay 205, contacts 245 ot relay 230 and to ground at contacts 246 ot relay 217. When relay 240operates it closes a circuit to hold relay '209 energized. which circuit may be traced trom battery, winding of relay 209, contacts 293 of relay 240, contacts 290 ot relay 209, contacts 291 of relay 207, contact-s 2920i relay 219 to ground. Relay 240, in operating, also reconnects the operator to the repeating coil and recloses the circuit `for the supervisory relay CS, thus operating the relay 284 and again putting out the supervisory lamp C.

When the plug is withdrawn' Ytroni the jack the second time, relays 202 and 210 release, all other relays ,being locked up. Vhen relay 210 releases it removes a shunt, around the windings of relays 281 and 227 g not hold operated and they, therefore,V re v lease'. Relay 281, however, operates in this circuit and at its contacts 294 supplies ground to hold relay 225 operated,v which would otherwise release when relay 230 released. This circuit can be traced trom batte1y,u'iiitliiig of relay 225, contacts 277 of relay 205, and contacts 294 of relay 281 to ground. Y

By reason of the fact that the energizing circuit for the supervisory relay 384 at thev distant exchange is completed through the malte contacts 385 of relay 331, it willKL be evident that the alternate release and operation" ot' relay 331 dueto the alternate increase and decrease of the trunk 're sistance caused by the calling operators alternate plugging out and in, will cause the distant calledv operators cord supervisory AS toV follow the removal and insert-ion of the plug at thecalling end, thus causing lamp A to tlashto indicate to the operator that she is Wanted.

Disconnecz'on.

lVhen the conversation is completed and the plug at the calling end is removed, the distant operators supervisorylamp A will be steadily lighted as will be evident from the above description. When, the called operator removes plug AP from jack 301, re-

lays 302 and 384 are released, followed by relays 309 and 310. lVhen relay310v releases, relay 331 and its associated battery is disconnected from the trunkVr and when relay 310 completes its back contacts 337. relays 331 and 327 are connected in series with 327 and holding` relay 331 operated. lVhen relay 327 operates it connects battery through resistance 362 to thetrunk in place of through relay 331 and y also relayf327, in operating, breaks at its contacts 326 the ll() each other and battery, thus operating relay y leasing -relay 281 at the calling end ot the trunk. Relay 281, in releasing, opens the holding circuit of relay 225 which releases and causes theY returnto-normal otall rref' lays at the calling end.` Both ends oi the trunk are now in normal condition.' When pluf` 200 at the calling exchange was removed supervisory relay CS released andV cuits. a bridge at each end ot said trunk line for controlling its associated signal, means including electrical current for controlling.

said bridge, and means controlled by the operator originating therconnection for causing the application of they current to be shitted from one end of the trunk tothe other. y

2. In a telephone exchange system, a trunk line, an operators position at each end ot said trunk line, a cord circuit'at each ot said operators positions connected to the trunk line, a signall for each of said cord circuits, a bridge at each end oi" said trunk line -for controlling itsassociated signal, means including electrical current for controlling said bridge, and means operated in response to flashing by the operator originating the connection for shifting the anplication or' current from one end of the trunk to the other and for maintaining the trunk busy during the flashing period.

8. In a telephone system, a trunk line extending between operators positions ot' two exchanges, a. supervisory circuit, sources of current therefor, one ot' said current sources being` connected in said circuit at the originating operators position upon the establishment of a connection between operators over said trunk line, and means responsive tothe disconnection from and reconnection to the trunk by the operator originating the connection for disconnecting said one source of current from the originating position and connecting the other of said sources to the distant operators position.

4i. ln a telephone system, a trunk extending' between two exchanges. operatorsy link circuits thereat adapted tov be connected to each end ot said trunk, a supervisory signal associated with each link circuit, a circuit for said signals including a source ot current completed when both of said link circuits are connected to the trunk, said source of current being connected in said circuit at the exchange originating the trunk connection, and means responsive to the disconnection from the trunk and the reconnectionV thereto oit the link circuit at the originating exchange for removing said current source v said operators positions, sources ot' current p therefor, one of said current sources being connected in said supervisory circuit at the o )erators ositon orioinatinc the establish` nient oi a connection, and-means responsive to the disconnection `from and reconnection to the trunk by vthe operator originating the connection, while the distant operator is connected to the trunk, for disconnecting said one-source of current troni the originating operators position and connecting another Vot' said sources ot current in said circuit at the distant operators position. f

6. In a. telephone exchange system, a two way inter-exchange trunk, an operators cord circuit adapted to be connected to each end thereof to establish an inter-exchange connection, a supervisory signal circuit including direct current extending between cord circuits over said trunk when said inter-exchange connection is established, said current being connected in they supervisory circuit at the exchange originating the inter-exchange connection, and means responsive tothe removal and insertion of the originating exchange cord circuit plug for transferring vthe connection of current Jfrom the originating to the called exchange end of the supervisory circuit.

7. In a telephone system, a calling and a called exchange, a two-way trunk line therebetween, a battery connected therein at the callingexchange upon connection to said trunk by said calling exchange, and automatic means responsive to disconnection Vtrom the trunk by the calling exchange after the called exchange has connected with the trunk for holding said trunk busy at the calling end for disconnecting said battery at the calling end and for connecting a similar battery in the trunk at the Vcalled exchange. y

8. In a telephone system, a trunk line extending between a calling operators position at one exchange and acalled operators A position at another exchange, operators rcord circuits thereat adapted to connect to each end of said trunk, supervisory signals associated with said cord circuits, a source of current for controlling said signals, and means, actuated by the disconnection of the vcord circuit from the trunk atvthe calling exchange while the cord circuit at the called exchange is connected to the other end of the trunk, for holding the trunk` busy at the calling end during the period that said operators cord circuit at said calling exchange disconnected vand said opeiators cord cir position at another exchange, operators cord circuits tlieieat adapted to connect to each end oi said trunk, supervisory signals associated with said cord circuits, a source of current controlling' said signals associated with said trunk at the called end thereof upon disconnection therefrom of the calling operators cord circuit While the called operators cord circuit is connected to the trunk, and a relay in series With said source of cnri-ent i'ior causing` lsaid trunk to test busy at tlie calling end duringthe period that said callingl operators cord circuit is disconnect-y ed from the trunk and said called operators cord circuit is connected thereto.

l0. In a. telephone system, trunk lines ex tending between operators positions inl tivo exchanges'. a supervisory circuit and sources of current therefor, one of said' current sources being' connected to saidv circuit at nection for holding said trunk bus)7 at the originating exchange during the period that said connection is broken tliereat and the connection With said trunk is maintained at` the distant operators position, and ineans also responsive to the breaking of the originating operators connection for disconiiectingsaid one source of current Jfrom lthe originating end of said circuit and Vfor connecting anotherV of said sources of current in said circuit at the distant operators po- Sition. v

In Witness whereof I' hereunto subscribe iny naine this 14th day of September A. D., 1923. 1

VARREN XV. CARPENTER. 

